F.C.G. Müller (same as Hubner and Post) made the barium salt of ortho brom toluene sulphonic acid, and then removed the bromine by treatment with sodium amalgam. The excess of alkali was removed by sulphuric acid, the sodium sulphate removed by evaporation and crystallization, and the residue dried. On treatment with phosphorus pentachloride an oily toluene sulphonchloride was obtained; this was decomposed by heating with water, the hydrochloric acid removed by repeated evaporations, and the syrup thus obtained evaporated to a crystalline condition. Several salts were made and studied. His amide melted at 90-91. Because this acid differed in properties from the two previously mentioned, Müller considered it to be the meta toluene sulphonic acid.
About this time F. Gervor (Ann. chem. (Liebig) 169,383), made ortho diazo toluene sulphonic acid by subjecting ortho toluidine sulphonic acid to nitrous fumes. This was decomposed with alcohol under pressure, and a sodium salt of the acid obtained; this was converted into the chloride and an amide which melted at 148, differing in this and other properties from the amides of the ortho and para toluene sulphonic acids previously known.
In 1874 Pechmann (Ibid., 173,195) obtained a quantity of para toluidine meta sulphonic acid by heating para toluidine with sulphuric acid, and crystallizing out the para toluidine ortho sulphonic acid and disulphonic acids, leaving the meta acid in solution because of its greater solubility. The diazo compound was made by treatment of the acid in alcoholic suspension with nitrous fumes, and decomposed with alcohol under pressure. Various salts of the resulting sulphonic acid were made and studied, also the chloride and amide which melted "somewhere below 100".
In 1875 Pagel (Ann. chem. (Liebig) 176,297) working on ortho toluidine sulphonic acid, made a toluene sulphonic acid which resembled Muller’s. His amide melted at 104.
In 1877 Beckurts (Ber.d.che. Ges. 10, 943), seeking for a good method of obtaining pure ortho toluene sulphonic acid, heated toluene and sulphuric acid in the ordinary way, and made the potassium salts of the resulting acids. By treatment with phosphorus pentachloride he obtained the acid chlorides which he separated by cooling to -15, and filtering off the solid para compound. The remaining liquid was transformed into an amide and purified by fractional crystallization. Two compounds were obtained with sharp melting points of 153 and 104. From this work he concluded that the sulphonation of toluene yielded all the three possible acids.
Fahlberg (Am. Chem. J. 1, 170), doubted Beckurts’ statement, because although his acid showed different properties he neglected to prove its constitution by converting it into the hydroxy benzoic acid. He therefore repeated Beckurts’ work, and identified the amide melting at 154 as coming from ortho toluene sulphonic acid, by conversion into salicylic acid. The other amide with a sharp, constant melting point of 108 was oxidized, and the products separated and identified as para sulphamine benzoic acid, anhydro ortho sulphamine benzoic acid, and acid potassium ortho sulphobenzoate. These were the products one would expect from an oxidation of a mixture of the ortho and para toluene sulphonamides. Further proof that his acid was a mixture was obtained by mixing amounts of pure ortho and para toluene sulphonic acids, and by repeated crystallizations a form was obtained which melted at 108.
F.H.S. Muller (Ber. d. chem. Ges. 13, 1348), mentioned the formation of meta toluene sulphonic acid by the action of sulphurous acid upon the corresponding diazo compound, but gave no details except the melting points of his amide, anilide, and toluide.
Claesson and Wallin in 1879 (Ibid. p. 1848), claimed that they had obtained meta toluene sulphonic acid by the action of chlorsulphonic acid upon toluene. They used very large quantities of materials. They obtained three acids, and identified them as the ortho and para, and called the third the meta acid, despite the fact that they had knowledge of Fahlberg’s work.
The next step was undertaken by R. Otto (Ibid, 13, 1292), at the request of Beckurts. He examined some of the latter’s supposed meta toluene sulphonamide, and found it to be a mixture of the amides of the ortho and para acids.
Nevile and Winther (Ibid. 13, 1940), while investigating the formation of amino sulphonic acids, obtained a toluene sulphonic acid by heating ortho diazo toluene sulphonic acid with alcohol under pressure, and also by reducing brom toluene sulphonic acid with sodium amalgam. It was converted into the chloride and amide,—the latter melting at 106.5-107.5.